Cementitious compositions



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Patented Dec. 8, 1953 2,662,024 CEMENTITIOUS COMPOSITIONS Wallace 0.Ridden, Berkeley, and George B. Kirk,

Redwood City, Caliit, assignors, by mesne asuignments, to Kaiser GypsumCompany, Inc, a corporation of Washington No Drawing. Application March1, 1951, Serial No. 218,488

11 Claims. (01. 106-109) This invention relates to cementitiouscompositions; and particularly to such compositions for use with gypsumwallboard, especially fg wng thejointsbet "'1 aces of the boards afterinstallation.

I In order to produce a monolithic effect in a construction using gypsumwallboard it is necessary to treat the joints between boards, nail headsand any other surface defects so that a smooth, uniform surface results.Cementitious or adhesive materials have been proposed for these purposesin the prior art, but have had some disadvantages. Many suchcompositions have had a protein base, for example, but this 'type ofadhesive requires considerable waiting time, for instance, to minutes,after mixing the dry powder with water, to allow the "protein to go intosolution. In some commercial cements a marked change in con-- sistencyoccurs during the waiting period so that it is necessary to readjust theconsistency by mix- 'ing in more dry powder to obtain a workable paste.A strongly alkaline pH is also essential in employing such a material.This strongly "alkaline condition is quite disadvantageous inapplication to wallboard because it is injurious to the paper coveringof the board, resulting in weakening of the paper and marring itssurface appearance. In other practices of the prior art, farinaceoussubstances have been employed in such compositions, but it has beennecessary to use only small portions because of the increased tendencyto cause cracks and checks in the surface, which remain even after thesurface has 'been painted. The tendency to crack and check also occursin the same manner with the proteincontaining materials which alsoshrink appreci- {Jbly in drying.

Ihe above disadvantages are overcome by the 'cementitious composition ofthe present inventionrand still fm-ther advantages are obtained.According to the present invention there is pro- -vided a eemeptitiouscp msigon, or a cement 2!. leinl nhetueenjle l li and for providing asmooth, uniform surface for wall- ;boards,co n ta in 'n 1g from todeadburned 50 17 5? dextrin, i'r'om 5% .sum from 15 mica from of glaz.from 10% to 2 o o 10% -to 20 ,0 of and less than .0% of b s, iortlangcemen fiferably, the cementitious composi 1011 a 0 contains from 0.5% to2% of a or from 0.2% to 1.0% of a dispersin aent, wetting agen or,advantageously, both of these g e en s. Alternatively, if desired, thewetting agent or the dispersing agent, or both, can be 2 added to themixing water at the time and place of use of the composition.

The composition is employed as a finely divided powder, according to theusual good practice'in this art. In use, Will-m to asmo u andcan e appzed to the joint. r surface immediate y. e. g. h e oints betweenadjacent edges of wallboard or in covering nail heads or surface defectsin the board. Any paste which remains unused at the end of a working daycan be retempered, that is, mixed with water to the desired consistency,replacing water lost by evaporation, on the following day, and can bethen employed in the same manner as freshly prepared paste. Thecementitious paste is applied to the wallboard joint or surface and setsto a hagiygmpositionjn a short miter example ii about 2 to 3 hours,igpeni; i h w nnconnlncmldu in,lar ema t o @tting of the degtrincomponent: upon Luther 'ment slowly sets also, forming a strong mass ofinterlaced gypsum crystals, providing still further increased strength,hardness, and waterand heat-resistance.

The deadburned gypsum employed is Keene's cement or other deadburnedgypsum w o so very slowly and is not sensitive to atmospheric moisture.Keane's cement, for example, is well known to the art and comprises acalu dmemww a m QLlZ OiE- 0 5 1% which after calcining is ground tosubstantially pass a mesh screen, and then usually a small amount of acc elerator is added, for instance less than about 1% of aluminum sulfateor potassium .sulfate, or of each when both are added. Such material,because it sets slowly in the cementi- 'tious composition, provides lateand increased strength in finely divided form in order to provide asmooth suri'ace when set. Suitably, this gypsum can be of a size tosubstantially entirely pass a 100 mesh screen. The dextrin component is,for example, a ggxtrinizemstarch. or it can be a mixture of dex 1' an am or portion, up

na 11mm, e wei ht or h c mmp artiall inized starch which, for example,ca n c' ontE rom 217 a 5' 40% water-soluble a I J tXAMINtH ized starchare particularly advantageous because they provide desired bulkiness. Ina preferred embodiment, a dextrin component as described i mployed l caon pel by ei t of dextrin and 3 parts by weigh t g f partifll y deg;-..trinized .starch, or modified corn flour as it is sometimes known inthe trade, these weights being based on the total weight of the jointcement mixture. The dextrin is a product made, for example, by treatingcorn starch with acid in a water medium, with heating, to convert todextrin. After the conversion is finished, the fluid is neutralized,dried and ground. Starches other than corn starch can be employed inmaking the dextrinized or partially dextrinized product. The starchycomponent gives a much harder and stronger early set in the compositionof this invention.

The clay employed is a plastic clay, preferably commercial fire cla andis also used in finely divided form. It improves the workability of thepaste so that it can be readily applied or "buttered on the surface tobe treated.

Mica is also employed in finely divided form and it is of specialadvantage in a composition containing the hereinabove-defined amounts ofdextrin component. The use of these high amounts of the dextrincomponent produces a strong and hard composition but, in the absence ofthe amount of mica defined, the dried cement exhibits shrinkage cracksor checking. It has been found that these cracks and checks aresubstantially entirely eliminated by the addition of the mica in theamounts shown, especially in cooperation with the amount of asbestosadded. Furthermore, the adhesiveness of the composition is apparentlyimproved by the mica addition. The asbestos fiber forms a fibrous mat inthe composition which enables uniform drying of the composition withmore uniform development of strength and desired surfacecharacteristics, and ,aids in the prevention of cracking and checkingupon drying.

A small amount of Portland cement, that is, less than 1.0%, and pre cm aout 0.2% to about 0.3%, is included in the composition. This acts tomaintain a slightly alkaline reaction, which is found to prevent rustingof nailheads in contact with the cement, but at the same time thealkalinity is maintained well below that which causes damage to paper,especially the paper a liner or covering of gypsum wallboard. It is onetheory of the operation of the Portland cement addition, but withoutintention of being limited by this theory, that this cement in thepresence of water hydrolyzes slowly to form an amount of Ca(OH)z whichmaintains the desired alkalinity. At the same time Portland cement isstable when stored in air, whereas if an equivalent amount of calciumhydroxide were added in the mix, it would absorb carbon dioxide from theair to form the carbonate, reducing its effectiveness. The Portlandcement irrthe co rppsiginpilthis iurTnupirisad edlin sufiicient qnaimlatain the alkalinity thereof atlrom more than pH 7.0 isiesstheirpn 8.0?when in the presence pf water.

Preferably a dis ersin a ent is also included -with the cementitiouscomposition of this inefiective constituent. In this specification andclaims the agent will be termed waste sulfite liquor. There can also beemployed herein a purified lignin derivative of wood which has beendigested with caustic soda or sodium sulfite, to

- produce cellulose pulp. This lignin derivative is preferably employedin the form of the watersoluble sodium salt. This lignin derivative andits sodium salt are described in a brochure entitled Indulin: Ligninfrom Pine Wood," published by West Virginia Pulp & Paper Company.Alternatively, also, there can be employed in this invention adispersing agent which is a watersoluble salt of a condensed a lsulfonic acid, such as the sodium salt of condensed mononaphthalenesulfonic acid. The dispersing agent is preferably added in an amount offrom about 0.5% to about 2.0% by weight, based on the total weight ofthe mix; and it can be added in the dry state, or an equivalent amountof liquid.

Preferably a wettin agent is also included with the above-desmtitiouscomposition. The wetting agent can be included in the compositionitself. Alternatively, the wetting agent can be incorporated in thetempering water, if desired, along with the dispersing agent describedabove, and this mixture can be added to the dry mixture of ingredientsdescribed above, to form the pasty mass for application to the wallboardjoint or surface. The wetting agent is, for

example, an alk 1 ar 1 sulfonate, such as a WW lsu lfona te, afi'alElated monoso mm c zene su onate, or the like. Any other desired wettingagent can be employed. The wetting agent wets out the paper liner of thegypsum board, promoting bonding of the cement thereto. The wetting agentis preferably added in an amount of from about 0.2% to about 1.0% basedon the total dry weight.

It is an advantage of the present invention that the composition setsfairly rapidly to give a hard cement with a high early strength; andanother advantage is that the deadbumed gypsum, or Keenes cement, setsmore slowly providing continually increasing strength and a final veryhard and strong product. It is believed that some of the Keenes cementcombines with the sugars present in the dextrin or partially dextrinizedstarch to form insoluble calcium saccharate. which enhances the strengthan ardness of the final product. It is a further and particularadvantage of this composition that the incorporation of mica preventscracking or checking so successfully that relatively large amounts ofdextrin can be incorporated to give the enhanced early strength andhardness, and that the final surface is smooth and continuous, asdesired. It is also an advantage that the material can be mixed withwater and used immediately. Further advantages will be noted from theabove description.

A specific example of a cementitious composition according to thepresent invention is as follows:

Per cent Keenes cement, substantially entirely passing 100 mesh 47.00Dextrin 17.00 Partially dextrinized corn flour 3.00 Mica, powdered 15.00Asbestos fiber, finely ground 10.00 F'ireclay, finely ground 7.00Portland cement 0.25 Waste sulfite liquor (dry) 0.50 Wetting agent(alkyl aryl sulfonate) 0.25

The partially dextrinized corn flour used in this example is of suchconsistency that it requires, per 100 grams thereof, the admixture offrom 500 to 600 milliliters of water to form a paste which will justpour.

The amounts in this specification and claims are expressed inpercentages by weight, based on the total dry weight of the mixture, or,in other words, not including water employed in mixing. Where screen ormesh sizes are given herein, they are in meshes per linear inch, U. S.Bureau of Standards screens.

Having now described the invention, what is claimed is:

1. Cement for wallboard joints and surfaces containing from 35% to 50%of finely divided deadburned gypsum, from 15% to 20% of dextrin, from 5%to of finely divided clay, from 10% to 20% of finely divided mica, from10% to 20% of finely ground asbestos, and a small amount of Portlandcement, said Portland cement being present in an amount of less thanabout 1%, said percentages being based on the total weight of themixture.

2. Cement for wallboard joints and surfaces containing from 35% to 50%finely divided deadburned gypsum, from to of dextrin, from 5% to 10% oifinely divided plastic clay, from 10% to 20% of finely divided mica,from 10% to 20% of finely ground asbestos, a small amount of Portlandcement, said Portland cement being present in an amount of less thanabout 1%, from 0.5% to 2% of a dispersing agent, and from 0.2% to 1% ofa wetting agent, said percentages being based on the'total weight of themixture.

3. Cement as in claim 2 wherein said dispersing agent is dried wastesulfite liquor.

4. Cement as in claim 2 wherein said wetting ent is a sodium salt ofanal}; l a l 5. Cement as in claim 2 containing from 0.2% to 0.3%Portland cement.

6. Cement as in claim 2 wherein the dextrln includes up to about 15% ofthe weight of this component of partially dextrinized corn starch.

7. Cement for wallboard joints and surfaces containing from to 50%finely divided deadburned gypsum, from 15% to 20% of dextrln, from 5% to10% of finely divided plastic clay, from 10% to 20% of finely dividedmica, from 6 A 10% to 20% of finely ground asbestos, a small amount ofPortland cement and from 0.5% to 2% of a dispersing agent, said Portlandcement being present in an amount of less than about 1%.

8. Cement for wallboard joints and surfaces containing from 35% to 5finely divided deadburned gypsum, from 15% to 20% of dextrin, from 5% to10% of finely divided plastic clay, from 10% to 20% of finely dividedmica, from 10% to 20% of finely ground asbestos, a small amount ofPortland cement and from 0.2% to 1% of a wetting agent, said Portlandcement being present in an amount of less than about 9. Cement forwallboard joints and surfaces containing from 35% to 50% finely divideddeadburned gypsum, from 15% to 20% of dextrln, from 5% to 10% of finelydivided plastic clay, from 10% to 20% of finely divided mica, from 10%to 20% of finely ground asbestos, and a small amount of Portland cement,said Portland cement being present in an amount of less than about 1%,and having a pH of from more than 7.0 to less than 8.0 in the presenceof water,

said percentages being based on the total weight of the dry mixture.

10. Cement for wallboard joints and surfaces containing from 35% to 50%finely divided deadburned gypsum, from 15% to 20% of dextrin, from 5% to10% of finely divided plastic clay, from 10% to 20% of finely dividedmica, from 10% to 20% of finely ground asbestos, a small amount ofPortland cement, said Portland cement being present in an amount of lessthan about 1%, from 1% to 2% of a dispersing agent, and from 0.2% to 1%of a wetting agent, said percentages being based on the total weight ofthe mixture, said cement having a pH of from more than 7.0 to less than8.0 in the presence of water.

11. Cement for wallboard joints and surfaces containing 47% of Keenescement substantially entirely passing mesh, 15% finely divided mica, 10%finely ground asbestos fibers, 7% finely divided fire clay, 17% dextrin,3% partially dextrinized corn starch, 0.5% dried waste sulflte liquor,0.25% of a sodium salt of an alkyl aryl sulfonate and 0.25% of Portlandcement, said percentages being based on the total weight of the mixture.

WALLACE C. RIDDELL. GEORGE B. KIRK.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,194,926 Anderson Aug. 15, 1916 1,858,369 Linzeli May 17,1932 1,863,990 Nelson June 21, 1932 2,127,451 scripture Aug. 16, 19382,318,540 Talbert May 4, 1943 2,322,930 Gardner June 29, 1943

1. CEMENT FOR WALLBOARD JOINTS AND SURFACES CONTAINING FROM 35% TO 50%OF FINELY DIVIDED DEADBURNED GYPSUM, FROM 15% OF FINELY DIVIDED FROM 5%TO 10% OF FINELY DIVIDED CLAY, FROM 10% TO 20% OF FINELY DIVIDED MICA,FROM 10% TO 20% OF FINELY GROUND ASBESTOS, AND A SMALL AMOUNT OFPORTLAND CEMENT, SAID PORTLAND CEMENT BEING PRESENT IN AN AMOUNT OF LESSTHAN ABOUT 1%, SAID PERCENTAGES BEING BASED ON THE TOTAL WEIGHT OF THEMIXTURE.